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earthing issue

Discussion in 'Amps and Cabs [BG]' started by Booster, Sep 7, 2008.

  1. Booster


    Jun 3, 2008
    New Zealand
    ok I know its most likely in the wrong area .. but hey

    right I have a genz-benz shuttle 6.0 12t and a warwick quad cab and a warwick corvette $$ and for some reason im having a serious earthing issue (well I think it is) it buzzes like nothing else if you touch the volume or tone knobs then it stops if you touch anything metal on the head it stops had our practice pa in the same power outlet .. buzzed then touched the head of my mic and it stopped hmm all the gear is less than 2 months old only giged twice should I just bite the bullet and take it back to where I bought it (most likely wont get it back for at least a month) I really hope its something simple if you guys have a clue wat the prob is that would be great..

  2. hasbeen

    hasbeen Commercial User

    Sep 23, 2004
    Vice President, KMC Music. Warwick U.S. distribution, Ampeg distribution
    I'm having a very tough time understanding that way you describe your challenge...but I'll try to help.

    The grounding problem most likely has nothing to do with the amp. It is more likely a ground in your bass. If it were your amp and/or other ac powered gear, it would be more of a hum.....is in ground loop hum.

    Have you tried a different bass? ...a different cable?

    Unfortunately, diagnosing grounding problems takes LOT of experimenting....you have to change all the variables...different outlet, different cable, different instrument...etc.
  3. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    If the 'volume and tone knobs' you're refering to are those on your bass it indicates a bad ground connection within it.
  4. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Have an electrician check the power (all receptacles) in your rehersal space for proper grounding. Since this happens with your bass and your practice PA, it's unlikely that it has anything to do with your bass amp.

    If your bass has missing internal grounding (specifically the bridge bonding to the shield and the internal cavity/control bonds) any groundingproblem will be exaggerated.
  5. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    If the buzz stops when you touch both the bass and the amp, or other grounded (earthed) object on same outlet, it is almost certain to be the bass.

    When you say it also stops if you touch the CONTROLS on the bass, it sounds like the shielding for the cavity around the controls, and /or the strings are not correctly connected to the cable shield, or that there IS no cavity shielding around the controls.

    What is happening is probably that your body picks up the 60 (or 50) hz buzz from the mains, and capacitively 'couple" that into the signal wiring of the bass. When you touch something earthed, that mains buzz signal is bypassed to earth, and your body is at earth voltage, no longer able to couple the buzz into the wiring.

    The usual rule is that strings and cavity shield are all connected to the "sleeve" on the cable plug, which is the shield of the guitar cord.

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